Della Chiesa, who held a doctorate in civil law from the Royal University of Genoa, won election as Pope on September 3, 1914, shortly after the outbreak of war. From the beginning, Benedict XV called upon the warring parties to end the conflict. His first encyclical, Ad Beatissimi, took an unequivocal stand against the war and associated war with Satan's envy of the Kingdom of Peace. Benedict then strove relentlessly to end the war and to prevent Italy's entry into the hostilities.

Although Pope and Church were accused widely of pro-Austrian neutrality, Italy's Catholics supported the Pope's neutralism. Moderate and liberal Italian Catholic laypersons and the radical peasant White Leagues of the Po Valley joined pro-Vienna aristocrats in demanding an end to the war and Italy's absolute neutrality. They were joined by the vast majority of Italian Socialists and by most liberals. Yet, owing largely to Benedict's and the Church's inability to act in any other than the most conservative diplomatic manner, Italy's intervention and the widening of the war could not be prevented by popular forces. To have sponsored or allowed the kinds of mass actions undertaken by the Socialists, for example, was unthinkable to the practitioners of Vatican diplomacy.

Benedict maintained rigorously his anti-war position and sought on several occasions to facilitate a diplomatic settlement. Most importantly, he proposed in August 1917 a plan based upon the prewar status quo. In the proposal, he cited the "useless carnage" of the war. While the proposal won few adherents in ruling circles, Benedict's rhetoric was blamed and credited for having helped to inspire the insurrection against the war in Turin later the same month. As the end of the war approached, Benedict lost the peace-making mantle to Woodrow Wilson.

Later years found the Pope in support of the Washington Naval Conference and in favor of aid to lessen suffering in war-torn Russia.